Yes. You can fully customize your packing slips, including the font sizes.
For more information about customizing your packing slips, take a look at our set up guide.
FAQs: Packing Slips
How to: Set up your Packing Slips
How to: Print packing slips with my shipping labels
How to: Create a custom Packing Slip Template and save it to your settings
How to: Design a custom Packing Slip Template